This invention generally relates to photographic film cartridges for use in cameras of the self-developing type, in which photosensitive materials exposed within a camera are developed by a diffusion process upon withdrawal from the camera. It particularly relates to film packages for cameras in which a plurality of multilayered photographic film units are stored in a flat configuration in a cassette which retains such film units in position to be exposed with a photographic apparatus.
Cassettes which are capable of retaining instant self-developing film units are generally flat elongated containers having an exposure opening in the forward wall through which light from the scene being photographed can be focused and an exit opening formed by the top wall through which a film unit can be withdrawn from the container subsequent to exposure for processing.
Each film unit includes a negative and a positive element in the form of a pair of sheets each of which has a photographic coating on one surface, and the format may be such that the sheets are in superposed relationship with the coatings of each sheet facing in the direction of the exposure opening. In any event, the coating of the sheet which is photosensitive must be oriented toward the opening in the film container. A pressure plate is usually located between the elements to urge the sheet containing the photosensitive coating into a plane that coincides with the focal plane of the camera into which the film package is inserted. Web means inter-connect the sheets and are cooperable with the pressure plate so that the sheet containing the image receiving coating can be longitudinally moved relative to the container until it is positioned in registration with and adjacent to the other sheet with the coated surface of each facing the other. In this condition the sheets are in contacting registration, and the introduction of processing liquid between them effects the transfer of image forming materials from the photosensitive coated sheet to the image-receiving sheet. The introduction of such processing liquid takes place when both sheets are longitudinally moved as a unit through the exit opening of the cassette and between a pair of pressure rolls mounted within the casette-containing photographic apparatus. The construction may be such that initial movement of the sheets as a unit fractures a pod holding the processing liquid and attached to the film unit. Upon withdrawal of the unit from the camera, and with concommittant spreading of the processing composition the diffusion of image-forming materials takes place outside the camera.
In certain embodiments of diffusion transfer systems and particularly certain systems which are capable of producing color images rather than black and white images, the film units are extremely gap sensitive; that is, they are very sensitive to variations in the distance maintained between the rollers as processing composition is being spread. Variations in effective gap in localized areas on the rollers, during processing of certain diffusion transfer products which may result from a manipulation of the exiting film unit rather than actual change in gap between the rollers, will provide unwanted chromatic effects in systems where the ultimate chromaticity of the photograph is a major function of the gap maintained between the rollers.
It has been found that with cassettes of the prior art, for example, the cassette shown in FIG. 3 of U.S. Pat. No. 3,479,181, as the photosensitive and image-receiving elements are caused to emerge therefrom, forward portions of the walls which constrain the film units against transverse movement can, in highly gap sensitive situations cause unwanted image areas if the film unit moves slightly transversely in exiting from the camera and an edge of the sandwich butts or rubs against a wall portion of the side walls of the cassette adjacent the exit opening. It is hypothesized that as this butting takes place, at a point somewhat removed from the area which touches the cassette, a change in effective gap is produced which, in a typical color film product will produce a redish orange unwanted spot or "pip". As has been alluded to, this change in effective gap is not due to any actual change in distance between the rollers, but to a bending or deforming of the film unit as it rubs against a cassette side wall when the film unit emerges from the camera. It has been found that by modifying the forward portions of the cassette walls which constrain retained film units against transverse movement by cutting away the portions of the side walls directly adjacent their sections which would ordinarily coincide with the exit opening these unwanted image areas are minimized nearly to the point of being eliminated.